1. Field of the Invention
The present invention relates to a corrosion preventing method in which a corrosion prevention current for removing corrosion of a contact is passed to remove corrosion of a contact, thereby preventing corrosion of the contact, and an apparatus for the method.
In the specification, “corrosion prevention current” is synonymous with a current for removing corrosion of a contact.
2. Description of the Related Art
In an apparatus which can detect a connection state of a contact of a switch, an erroneous determination and malfunction due to an increase of the resistance of the switch which is caused by corrosion of the contact become problematic. Recently, a corrosion preventing apparatus for removing corrosion of a contact has been put into practical use.
FIG. 29 is a circuit diagram schematically showing a contact corrosion preventing apparatus 1 which is disclosed in US 2005/0231858A. In the contact corrosion preventing apparatus 1, a comparator 6 compares the potential of a detection conducting path 5 which electrically connects a contact 3 of a grounded switch 2 to an electronic control section 4, with a predetermined potential VX. When the comparator 6 detects that the potential of the detection conducting path 5 is higher than the predetermined potential VX, the comparator detects corrosion of the contact 3. When corrosion of the contact 3 is detected, the output of the comparator 6 is set to Lo. A switching element 9 which is electrically connected to the detection conducting path 5 in parallel with a resistor 7, and which is electrically connected to a power source 8 is switched to a conduction state in which the terminals are conducting, thereby pausing a corrosion prevention current for removing corrosion through the contact 3.
FIG. 30 is a graph showing variation of the potential of the detection conducting path 5 with respect to an elapsed time. FIG. 31 is a graph showing output variation of the comparator 6 with respect to an elapsed time. In FIG. 30, the ordinate indicates the potential, and the abscissa indicates the time, and, in FIG. 31, the ordinate indicates Hi and Lo of the output of the comparator 6, and the abscissa indicates the time. In the contact corrosion preventing apparatus 1, when corrosion of the contact 3 proceeds, the potential of the detection conducting path 5 is raised. When the potential of the detection conducting path 5 becomes higher than the predetermined potential VX, the output of the comparator 6 is set to Lo to switch the switching element 9 to the conduction state, so that the corrosion prevention current is passed through the detection conducting path 5 and corrosion of the contact 3 is removed. When corrosion of the contact 3 is removed, the potential of the detection conducting path 5 is lowered. When the potential of the detection conducting path 5 becomes lower than the predetermined potential VX, the output of the comparator 6 is set to Hi to make the switching element 9 to a non-conduction state in which the terminals are not conducting, whereby a connection detection current which is used for detecting the connection state of the contact via the resistor 7, and which is smaller than the corrosion prevention current is passed through the detection conducting path 5 (see US 2005/0231858A).